In recent years, there has been known a communication system using a communication control protocol, such as SIP (Session Initiation Protocol). In the communication system using SIP, a plurality of terminals, such as IP telephone sets and FAX terminals, are connected to a SIP server, which performs SIP call control between an external apparatus and the terminals. The SIP server is comprised of a redirect server, a proxy server, a registration server and a location server.
For example, in a communication system in which FAX terminals are connected to the SIP server, specific FAX numbers and address information items (e.g. IP addresses) of the respective FAX terminal are registered in advance in association with each other in the SIP server (location server). When the SIP server receives a connection request to a specific FAX number from the external apparatus, in response to the request, the SIP server notifies the external apparatus of an IP address associated with the specific FAX number. The external apparatus having received the notification makes a connection request to the notified IP address, whereby a call is established between the external apparatus and the FAX terminal.
By the way, in the above-mentioned SIP server, it is possible to set a FAX machine (hereinafter referred to as “the second terminal”) different from the FAX terminal (hereinafter referred to as “the first terminal”) having an IP address associated with the specific FAX number, as a redirect destination (Patent Literature 1).
If the above setting is made, when the SIP server receives the connection request to the specific FAX number, the SIP server transmits an IP address of the second terminal in place of the IP address of the first terminal, although originally, the IP address of the first terminal is to be transmitted. This causes the external apparatus to make a connection request to the second terminal, and hence, as a consequence, the connection request to the first terminal is transferred or redirected to the second terminal.